Plastic containers such as bottles of water are manufactured and filled according to different methods including blow moulding or stretch-blow moulding.
According to one of these known methods a plastic preform is first manufactured through a moulding process and then heated before being positioned inside a blowing mould.
The preform usually takes the form of a cylindrical tube closed at its bottom end and open at its opposite end.
Once the preform has been positioned within the mould only the open end of the preform is visible from above the mould.
The above-mentioned method makes use of a stretch rod which is downwardly engaged into the open end of the preform so as to abut against the closed bottom end thereof. The stretch rod is further actuated to be urged against the closed end, thereby resulting in stretching the preform.
After the stretching phase has been initiated a liquid is injected into the preform through its open end during a filling phase, as disclosed for instance in Applicant's patent EP 1 529 620 B1. This liquid injection causes together with the stretching expansion of the preform until coming into contact with the inner walls of the mould, thereby achieving the final shape of the container.
The container that has been formed and filled with liquid, e.g. water, is then provided with a cap before being manipulated, shipped, stacked, carried, etc.
Typically bottles of water are grouped into packs or packages and then assembled together on a pallet.
Pallets are next transported in trucks or trains and may sometimes be stacked upon each other.
In such situations the bottles are exposed to strong external forces and loads and must be resistant thereto.
In particular, they need to be resistant to loads applied from the top.
If the mechanical strength of the container or bottle is not sufficient, the pallets may run the risk of collapsing, which could lead to rejection by the customer or even give rise to dangerous situations, accidents and possible injuries caused to people.
The trend from the market and consumers for sustainable and cost effective packaging solutions has been rising over the last years.
As a consequence, the beverage industry has reduced the quantity of material used in the manufacture of plastic containers, in particular bottles.
However, this reduction in material has come to its limits since the filled containers have to be resistant to strong external forces and loads as explained above.
There is therefore a need to increase the stability of containers.
One solution is to use more material for manufacturing the containers.
However, this solution goes against the above-mentioned trend.
Another solution is to add nitrogen or pressurized air in the filled container.
However, this solution involves an additional machine or piece of equipment and a further manufacturing step which requires, in particular, supplying a pressurized cleaned gas.
In addition, a specific container base or bottom part is needed for supporting this solution.
This requires additional material which is not appreciated by the consumers.